Polyolefin composition for medium/high/extra high voltage cables with improved electrical breakdown strength

ABSTRACT

This application relates to a polyolefin composition comprising a polyolefin and an aromatic compound. The polyolefin composition can be used in producing medium and high voltage cables with improved electrical breakdown strength.

This application is a Continuation of U.S. patent application Ser. No.12/809,990, filed Jun. 21, 2010, which claims priority to InternationalApplication No. PCT/EP2008/010913, filed Dec. 19, 2008, which claimspriority to European Patent Application No. 07024964.4, filed on Dec.21, 2007, the disclosures of which are herein incorporated by referencein their entireties.

The present invention relates to a polyolefin composition comprising apolyolefin with improved electrical breakdown strength, to a wire orcable, in particular a medium, high or extra high voltage cable,comprising such a composition, and to the use of such a composition forthe production of a wire or cable, in particular a medium, high or extrahigh voltage cable.

A typical medium voltage power cable, usually used for voltages from 6to 36 kV, a typical high voltage cable used for voltages higher than 36kV, and a typical extra high voltage cable used for voltages higher than170 kV, comprises one or more conductors in a cable core that issurrounded by several layers of polymeric materials, including an innersemiconducting layer, followed by an insulating layer, and then an outersemiconducting layer. These layers are normally cross-linked. To theselayers, further layers may be added, such as a metallic tape or wireshield, and, finally, outermost jacketing layer(s). The layers of thecable are based on different types of polymer compositions. Asinsulating materials, today cross-linked polyolefins like cross-linkedlow density polyethylene are predominantly used.

It is a constant aim of cable manufacturers to increase the electricalbreakdown strength of cable materials, in particular cable insulationmaterials, in order to achieve greater reliability and increasing energytransmission. To attain this aim, it is known to reduce the amount ofcontaminants in the insulation material. However, nowadays already superclean materials are used for insulation, and improvements in electricalbreakdown strength by further reduction of contaminants are associatedwith a significant increase in cost.

It is furthermore known to use active additives, namely so calledvoltage stabilisers, in order to increase the electrical breakdownstrength of cable insulation materials. For example, in U.S. Pat. No.3,482,033 it is disclosed to use a blend of non-volatile hydrocarbon oilof high aromatic content or a highly aromatic, low melting hydrocarbontogether with active voltage stabilisers such as polyhalopolyphenyls ornitro-group containing aromatics.

Furthermore, voltage stabilisers are known from WO 01/08166. In thisdocument, stabilisers based on benzophenone as core molecule substitutedwith alkoxy and phenoxy groups are disclosed.

However, there is still the need for voltage stabilisers which improvethe electrical breakdown strength of polyolefin compositions used formedium/high voltage cable isolation. Such compounds should usually havea low ionisation potential to decrease the energy of high energyelectrons and hence increase the electrical breakdown strengthefficiently (see e.g. A. C. Ashcraft, R. M. Eichhorn, and S. R. G.,“Laboratory Studies of Treeing in Solid Dielectrics and VoltageStabilization of Polyethylene” presented as I.E.E.E. InternationalSymposium on Electrical Insulation, Montreal, Canada, 1978).

At the same time, the compounds must be soluble in the polyolefin,usually cross-linked polyethylene, used as a matrix polymer in thecomposition, and, furthermore, must show low migration tendency, so thatthe loss of the compound in the insulation material with time is as lowas possible.

Still further, as usually insulating compositions are cross-linkedpolyolefins, the stabiliser must as far as possible be compatible tocommonly used cross-linking agents, such as organic peroxides, so that,on the one hand, the cross-linking process is not negatively affected,and, on the other hand, the stabiliser is not decomposed and thusinactivated. Of course, the stabiliser should also be compatible in thissense with regard to all other components of the polyolefin composition.

It is thus an object, to provide a stabiliser for improving theelectrical breakdown strength of a polyolefin composition, especiallyfor the use as an insulating composition in a medium/high/extra highvoltage cable, which has the above-mentioned properties, in particularprovides a significant improvement in electrical breakdown strength, haspreferably also a good solubility in the polyolefin matrix and a lowmigration tendency, and more preferably is compatible with regard toother components of the polyolefin composition, in particular tocross-linking agents.

It has now surprisingly been found that the above objects can beachieved by the use of a an organic compound as a voltage stabilisercompound which comprises an aromatic moiety which comprises anaphthyl-group or at least two phenyl-groups which are linked togetherso that no free rotation of one phenyl group with regard to the other ispossible, at said aromatic moiety of the compound there is present atleast one hydrocarbyl substituent which may comprise heteroatoms, andthe compound having at least one substituent which may compriseheteroatoms and which comprises at least 6 non-H atoms, with anyhydrocarbyl substituent which is attached to any aromatic moiety of thecompound being free of H-atoms in the alpha-position of the hydrocarbylsubstituent.

The present invention therefore provides a polyolefin compositioncomprising

-   -   (i) a polyolefin (A),    -   (ii) an aromatic compound (B) comprising a, preferably        consisting of the, structural unit according to the following        formula (I):

-   -   -   wherein        -   one or more of the C-atoms in the phenyl rings to which            residue R1, R2, R3, R4, R5, R6, R7, or R8 is attached may            also be a heteroatom, such as N, in which case the            respective residue R1, R2, R3, R4, R5, R6, R7, or R8 is not            present;        -   X either is no atom so that there is a direct bond between            the two phenyl rings, or is ═C(R11)-, —C(R11)₂-, —C(═Z)—,            ═N— or —N(R12)-,        -   Y either is no atom so that there is a direct bond between            the two phenyl rings, or is ═C(R13)-, —C(R13)₂-, —C(═Z)—,            ═N— or —N(R14)-,        -   Z is a divalent atom such as O,        -   R1, R2, R3, R4, R5, R6, R7, R8 and, if present, R11, R12,            R13 and R14 independently are hydrogen, or a hydrocarbyl            group which may contain heteroatoms;        -   or at least two of said R1, R2, R3, R4, R5, R6, R7, R8 or,            if present, R11, R12, R13 or R14, together with the ring            atoms of the ring system of formula (I) they are attached            to, form a further aromatic or non-aromatic ring fused to            the ring system of formula (I), and wherein the ring system            of formula (I) with said at least one fused further ring may            further bear one to eight substituents, R1′ to R8′, each of            which are independently selected from said same groups as R1            to R8;        -   with the provisios that        -   (i) at least one of said R1, R2, R3, R4, R5, R6, R7 or R8,            or if present, at least one of said R1′ to R8′, is a            hydrocarbyl group which may contain hetero atoms; and        -   (ii) at least one of said R1, R2, R3, R4, R5, R6, R7 or R8,            or, if present, said R1′ to R8′, R11, R12, R13 or R14, is a            hydrocarbyl group which may contain heteroatoms and which            has at least 6 non-H atoms;        -   (iii) if any of said R1, R2, R3, R4, R5, R6, R7 or R8, and,            if present, any of said R1′ to R8′, R11, R12, R13 or R14 is            a hydrocarbyl group which may contain hetero atoms, is            attached to an aromatic ring of the compound according to            formula (I), said hydrocarbyl group must be free of H-atoms            in the alpha-position;        -   and/or an aromatic compound with a, preferably consisting of            the, structural unit according to the following formula            (II):

-   -   -   wherein        -   one or more of the C-atoms in the naphtyl rings to which            residue R1, R2, R3, R4, R5, R6, R7, or R8 is attached may            also be a trivalent heteroatom such as N, in which case the            respective residue R1, R2, R3, R4, R5, R6, R7, or R8 is not            present;        -   or at least two of said R1, R2, R3, R4, R5, R6, R7 or R8,            together with the ring atoms of the ring system of            formula (II) they are attached to, form a further aromatic            or non-aromatic ring fused to the ring system of formula            (II), and wherein the ring system of formula (II) with said            at least one fused further ring may further bear one to            eight substituents R1′ to R8′;        -   and R1, R2, R3, R4, R5, R6, R7 and R8, and, if present, said            R1′ to R8′, have the same meaning and fulfil the same            provisios as indicated for formula (I).

The possible substituents X and Y in formula (I) inter alia definecompounds in which the aromatic system extends from the phenyl ring withsubstituents R1 to R4 (the first phenyl ring) to the phenyl ring withsubstituents R5 to R8 (the second phenyl ring). These compounds togetherwith the naphthalene compounds defined above are preferred embodimentsin the present invention. For example, the compound of formula (I) maybe an anthracene derivative, where X is ═C(R11)- and Y is ═C(R13)-, acarbazole derivative, where X is —N(R12)- and Y is no atom, or anacridine derivative, where X is ═C(R11)- and Y is ═N—.

However, the substituents X and Y in formula (I) also define compoundsin which the aromatic system does not extend from the first phenyl ringto the second phenyl ring. For example, the compound of formula (II) maybe an anthrachinone derivative, where both X and Y are —C(═O)— groups.

Furthermore, in formula (I) and (II) any of R1, R2, R3, R4, R5, R6, R7and R8 and, if present, R11, R12, R13, and R14 may also form a furtheraromatic or non-aromatic ring fused to the ring system of formula (I),and wherein the ring system of formula (I) with said at least one fusedfurther ring may further bear one to eight substituents, R1′ to R8′,each of which are independently selected from said same groups as R1 toR8. For example, R2 and R3 in formula (II) may form a—CR1′=CR2′-CR3′=CR4′- group, so that an anthracene derivative isobtained.

The term “hydrocarbyl group” denotes any substituent which is composedof carbon and hydrogen atoms regardless of the degree of saturation,e.g. alkyl groups, alkenyl groups, alkinyl groups and aromatic groupscomposed of C and H. Where it is indicated that a hydrocarbyl group maycontain heteroatoms these are atoms different from C and H, such as Si,N, P, O or S, typically N or O.

The term “hydrocarbyl group must be free of H-atoms in thealpha-position” means herein that the atom of the hydrocarbyl groupwhich is directly linked to an aromatic moiety of the compound accordingto formula (I) or (II) does not bear H-atoms.

It has been found that the use of the above compounds as stabiliseryields insulating polyolefin compositions with significantly improvedelectrical breakdown strength. The improvement in electrical breakdownstrength can be seen from the high values of the molar field stabilityas measured hereinafter. Furthermore, the compounds have a goodsolubility in the polyolefin matrix and a low migration tendency, andare inert with regard to other components of the polyolefin composition,in particular to cross-linking agents.

In an preferred embodiment said at least one of said R1, R2, R3, R4, R5,R6, R7 or R8, or, if present, said R1′ to R8′, R11, R12, R13 or R14mentioned in provisio (ii) to be a hydrocarbyl group which may containheteroatoms and which has at least 6 non-H atoms is selected from—O(R9), —N(R10)₂, wherein R9 and R10 independently are hydrocarbylgroups having at least 5 non-H-atoms.

In another preferred embodiment said at least one of said R1, R2, R3,R4, R5, R6, R7 or R8, or, if present, said R1′ to R8′, R11, R12, R13 orR14 mentioned in provisio (ii) to be a hydrocarbyl group which maycontain heteroatoms and which has at least 6 non-H atoms, is an aromaticgroup having at least 6 non-H-atoms and, preferably, contains asubstituent, i.e. the substituent is present at the aromatic group,which is a hydrocarbyl group which may contain heteroatoms.

More preferably, said substituent is selected from the groups of —O(R9),—N(R10)₂, wherein R9 and R10 are hydrocarbyl groups.

Preferably, in all embodiments the hydrocarbyl group mentioned inprovisio (ii) which may contain heteroatoms comprises at least 7 non-Hatoms, and more preferably comprises at least 9 non-H atoms.

Preferably, in the compounds with the structural units according toformula (I) or (II) all atoms in the phenyl or naphthyl rings to which aresidue R1 to R8 is attached are C-atoms.

It is furthermore preferred that R9 and R10 and, if present, R11, R12,R13 and R14, independently are a hydrocarbyl group which may containheteroatoms and has at least 6 carbon atoms, more preferably has 7carbon atoms, still more preferably at least 8 carbon atoms and evenmore preferably 9 carbon atoms.

Furthermore, preferably, R9 and R10 and, if present, R12 and R14,independently are an alkyl group, more preferably a straight alkylgroup, with at least 6 C-atoms, more preferably with at least 7 C-atoms,still more preferably at least 8 C-atoms, and most preferably at least 9C-atoms, which may or may not contain a functional group at the end,which, if present, preferably is a —CH═CH₂, a halogen, a hydroxyl,carboxylic acid or acid halide group.

Furthermore, preferably the compounds having a structural unit accordingto formula (I) or (II) are free of halogen substituents or substituentscontaining halogen atoms.

It is furthermore preferred that in the structural units according toformula (I) or (II) at least two hydrocarbyl groups as R1 to R8, or ifpresent, R11, R12, R13, and R14, which may contain heteroatoms, arepresent in any of their embodiments described before.

In such cases it is preferred that said two hydrocarbyl groups areseparated by at least two further ring atoms, e.g. are in para positionif the two groups are linked to the same phenyl group.

In a first preferred embodiment, the aromatic compound (B) has astructural unit in which in formula (I) X is ═C(R11)-, and Y is ═N—, sothat the compound is an acridine derivative having the followingstructural unit:

wherein R1, R2, R3, R4, R5, R6, R7, R8, and R11 have the meaning asdefined in any of the embodiments above.

In this first embodiment, it is preferred that two of R1, R2, R3, R4,R5, R6, R7, R8, and/or R11 independently are selected from the groups of—O(R9) and —N(R10)₂, and the remainder of R1, R2, R3, R4, R5, R6, R7,R8, and/or R11 are —H, wherein R9 and R10 have the meaning as defined inany of the embodiments above.

More preferably, the two of R1, R2, R3, R4, R5, R6, R7, R8, and/or R11which are not —H are connected to C-atoms which are separated by atleast two further ring atoms of the acridine ring system, for example R1and R4 are —O(R9), and R2, R3, R5, R6, R7, R8 and R11 are —H.

In this first embodiment, it is especially preferred that R5 and R11independently are —O(R9) or —N(R10)₂, more preferably —O(R9), and R1,R2, R3, R4, R6, R7, and R8 are —H; or that R3 and R6 independently are—O(R9) or —N(R10)₂, more preferably —N(R10)₂, and R1, R2, R4, R4, R5,R7, R8, and R11 are —H.

An example for and a preferred embodiment of the aromatic compound (B)of the first preferred embodiment is 4-methoxy-9-(octyloxy)acridine.

In a second preferred embodiment, the aromatic compound (B) has astructural unit in which in formula (I) X is ═C(R11)- and Y is ═C(R13)-,so that the compound is a anthracene derivative having the followingstructural unit:

wherein R1, R2, R3, R4, R5, R6, R7, R8, R11 and R13 have the meaning asdefined in any of the embodiments above.

In this second embodiment, it is preferred that two of R1, R2, R3, R4,R5, R6, R7, R8, R11 and/or R13 independently are selected from thegroups of —O(R9) and —N(R10)₂, and the remainder of R1, R2, R3, R4, R5,R6, R7, R8, R11 and/or R13 are —H, wherein R9 and R10 have the meaningas defined in any of the embodiments above.

More preferably, the two of R1, R2, R3, R4, R5, R6, R7, R8, R11 and/orR13 which are not —H are connected to C-atoms which are separated by atleast two further ring atoms of the anthracene ring system, for exampleR1 and R4 are —O(R9) and R2, R3, R5, R6, R7, R8, R11 and R13 are —H.

In this second embodiment, it is especially preferred that R11 and R13independently are —O(R9) or —N(R10)₂, more preferably —O(R9), and R1,R2, R3, R4, R5, R6, R7, and R8 are —H.

An example for and a preferred embodiment of the aromatic compound (B)of the second embodiment is 9,10-dioctyloxyanthracene.

In a third preferred embodiment, the aromatic compound (B) has astructural unit in which in formula (I) X is —C(═O)— and Y is —(C═O)— sothat the compound is a anthrachinone derivative having the followingstructural unit:

wherein R1, R2, R3, R4, R5, R6, R7, and R8 have the meaning as definedin any of the embodiments above.

In this third embodiment, it is preferred that two of R1, R2, R3, R4,R5, R6, R7, and/or R8 independently are selected from the groups of—O(R9) and —N(R10)₂, and the remainder of R1, R2, R3, R4, R5, R6, R7,and R8 are H, wherein R9 and R10 have the meaning as defined in any ofthe embodiments above.

More preferably, the two of R1, R2, R3, R4, R5, R6, R7, and/or R8 whichare not —H are connected to C-atoms which are separated by at least twofurther ring atoms of the anthrachinone ring system, for example R1 andR4 are —O(R9) and R2, R3, R5, R6, R7, and R8 are —H.

In this third embodiment, it is especially preferred that R1 and R4independently are —O(R9) or —N(R10)₂, more preferably —O(R9), and R2,R3, R5, R6, R7, and R8 are —H.

In a fourth preferred embodiment, the aromatic compound (B) has astructural unit in which in formula (I) X is —N(R12)- and Y is not anatom so that the compound is a carbazole derivative having the followingstructural unit:

wherein R1, R2, R3, R4, R5, R6, R7, R8, and R12 have the meaning asdefined in any of the embodiments above.

In this fourth embodiment, it is preferred that two of R1, R2, R3, R4,R5, R6, R7, and/or R8 independently are selected from the groups of—O(R9) and —N(R10)₂ or an aromatic group, preferably a phenyl group,which is at least substituted by at least one, more preferably one,—O(R9) or —N(R10)₂ group, with the substitution preferably being in aposition so that the atom of the aromatic group connected to thecarbazole body and the atom to which the —O(R9) or —N(R10)₂ group isattached are separated by at least two further ring atoms, e.g. are inpara position if the aromatic group is a phenyl group, R9 and R10 havethe meaning as defined in any embodiment above, and the remainder of R1,R2, R3, R4, R5, R6, R7, and R8 are —H.

Furthermore, R12 preferably is an alkyl group, preferably a straightalkyl group, and preferably has 1 to 50 carbon atoms, more preferablyhas 1 to 30 carbon atoms, still more preferably has 6 to 30 C-atoms, andstill more preferably has 8 to 30 C-atoms.

More preferably, the two of R1, R2, R3, R4, R5, R6, R7, and/or R8 whichare not —H are connected to C-atoms which are separated by at least twofurther ring atoms of the carbazol ring system, for example R1 and R4are —O(R9) and R2, R3, R5, R6, R7, and R8 are —H.

In this fourth embodiment, it is especially preferred that R3 and R6independently are an aromatic group, preferably a phenyl group, which isat least substituted by at least one, more preferably one, —O(R9) or—N(R10)₂ group, with the substitution preferably being in a position sothat the atom of the aromatic group connected to the carbazol body andthe atom to which the —O(R9) or —N(R10)₂ group is attached are separatedby at least two further C-atoms, e.g. are in para position if thearomatic group is a phenyl group, and R1, R2, R4, R5, R7, and R8 are —H.

An example for and a preferred embodiment of the aromatic compound (B)of the fourth embodiment is9-octyl-3,6-bis(4-(octyloxy)phenyl)-carbazole.

In a fifth, especially preferred embodiment, the aromatic compound (B)has a structural unit in which in formula (II) two of R1, R2, R3, R4,R5, R6, R7, and/or R8 independently are selected from the groups of—O(R9) and —N(R10)₂, and the remainder of R1, R2, R3, R4, R5, R6, R7,and/or R8 are —H, wherein R9 and R10 have the meaning as defined in anyof the embodiments above.

More preferably, the two of R1, R2, R3, R4, R5, R6, R7, and/or R8 whichare not —H are connected to C-atoms which are separated by at least twofurther C-atoms of the naphthalene ring system, for example R1 and R4are —O(R9) and R2, R3, R5, R6, R7, and R8 are —H.

In this fifth embodiment, it is especially preferred that R1 and R5independently are —O(R9) or —N(R10)₂, and R2, R3, R4, R6, R7, and R8-H.

An example for and a preferred embodiment of the aromatic compound (B)of the fifth embodiment are 1,5-dioctyloxynaphthalene orN1,N1,N5,N5-tetraoctylnaphthalene-1,5-diamine, withN1,N1,N5,N5-tetraoctylnaphthalene-1,5-diamine being an especiallypreferred embodiment.

It is preferred that in all of the above embodiments the aromaticcompound (B) consists of the structural unit described for theparticular embodiment. However, for all cases where the aromaticsystem(s) of formula (I) or (II) contain at least two substituents, itis also possible that structural units of any of the above describedembodiments are made into oligomeric structures, to increase themolecular weight.

For example, such an oligomeric compound based on1,5-dihydrocarbyloxynaphthalene as a structural unit would be

wherein R15 is an O(R9) group in any of the embodiments described above.

For example, in the case R15 is an n-octyloxy group and n=8 the compoundwould be the trimer of 1,5-dioctyloxynaphthalene.

It is furthermore possible and also within the scope of the invention toattach the aromatic compound (B) to one or more further components ofthe polyolefin composition of the invention, e.g. to attach it topolyolefin (A).

This may be done by copolymerising stabiliser-containing comonomers and“regular” monomers of e.g. polyolefin (A), or by grafting of suitablestabiliser compounds onto a polymer backbone.

Preferably, aromatic compound (B) is present in the composition in anamount of 0.001 to 10 wt %, more preferably 0.01 to 5 wt. %, still morepreferably from 0.05 to 4 wt. %, and most preferably from 0.1 to 3 wt.%.

Polyolefin (A) may be any polyolefin material suitable to be used forthe production of a layer of cable, preferably power cable layer, morepreferably an insulation layer of a power cable.

Polyolefin (A) preferably comprises or consists of a polyethylene orpolypropylene. Where herein it is referred to a “polymer”, e.g.polyethylene, this is intended to mean both homo- and copolymer, e.g.ethylene homo- and copolymer.

Where polyolefin (A) comprises or consists of a polyethylene, thepolymer may be produced in a high pressure process or in a low pressureprocess in the presence of a catalyst, for example a chromium,Ziegler-Natta or single-site catalyst, resulting in either unimodal ormultimodal polyethylene.

Where polyolefin (A) comprises or consists of a polypropylene, this maybe a unimodal or multimodal propylene homo- or copolymer and/or aheterophasic polypropylene.

Furthermore, where polyolefin (A) comprises or consists of apolypropylene, it is preferred that it has an MFR₂ (230° C., 2.16 kg) offrom 0.001 to 25 g/10 min.

In a preferred embodiment, polyolefin (A) comprises or consists of anethylene homo- or copolymer. In the case of an ethylene copolymer, it ispreferred that it includes up to 40 wt. %, more preferably 0 to 25wt.-%, even more preferably 0.1 to 15 wt.-% of one or more comonomers.

Preferably, the density of the ethylene homo or -copolymer is higherthan 0.860 g/cm³.

Furthermore, preferably the density of the ethylene homo or -copolymeris not higher than 0.960 g/cm³.

The MFR₂ (2.16 kg, 190° C.) of the ethylene homo or -copolymerpreferably is from 0.01 to 50 g/10 min, more preferably is from 0.1 to20 g/10 min, and most preferably is from 0.2 to 10 g/10 min.

Still further, it is preferred that polyolefin (A) comprises or consistsof a polyethylene which has been produced by a high pressure processusing free radical polymerization resulting in low density polyethylene(LDPE). The polymerization generally is performed at pressures of 120 to350 MPa and at temperatures of 150 to 350° C.

The LDPE may be an ethylene homopolymer or a copolymer of ethylene.

As a comonomer in the ethylene copolymer, a non-polar alpha-olefin maybe used, either alone or in addition with further types of comonomers.Such alpha-olefins may also comprise further unsaturation present e.g.in polyunsaturated comonomers such as dienes.

Preferably, C₃ to C₁₀ alpha-olefins without further unsaturation areused as comonomers, such as propylene, 1-butene, 1-hexene,4-methyl-1-pentene, styrene, 1-octene, 1-nonene and/or polyunsaturatedcomonomer(s) such as C₈ to C₁₄ non-conjugated dienes, such as a C₈ toC₁₄ non-conjugated diene, e.g. 1,7-octadiene, 1,9-decadiene,1,11-dodecadiene, 1,13-tetradecadiene, or mixtures thereof. Furthermore,dienes like 7-methyl-1,6-octadiene, 9-methyl-1,8-decadiene, or mixturesthereof can be mentioned.

It is preferred that the LDPE includes 0 to 25 wt.-%, more preferably0.1 to 15 wt.-% of one or more comonomers.

Polyolefin (A) preferably is cross-linkable. Cross-linking may beachieved e.g. by further including a cross-linking agent into thecomposition or by the incorporation of cross-linkable groups intopolyolefin (A).

In a preferred embodiment, the polymer composition according to thepresent invention further comprises a cross-linking agent.

In the context of the present invention, a cross-linking agent isdefined to be any compound capable to generate radicals which caninitiate a cross-linking reaction. Preferably, the cross-linking agentcontains at least one —O—O— bond or at least one —N═N— bond. Morepreferably, the cross-linking agent is a peroxide known in the field.

The cross-linking agent, e.g. a peroxide, is preferably added in anamount of less than 10 wt %, more preferably 0.1 to 5.0 wt. %, stillmore preferably 0.1 to 3.0 wt. %, even more preferably 0.15 to 2.6 wt.%, based on the weight of the cross-linkable polymer composition.

As peroxides as non-limiting examples of cross-linking agents are i.a.di-tert-amylperoxide, 2,5-di(tert-butylperoxy)-2,5-dimethyl-3-hexyne,2,5-di(tert-butylperoxy)-2,5-dimethylhexane, tert-butylcumylperoxide,di(tert-butyl)peroxide, dicumylperoxide,bis(tertbutylperoxyisopropyl)benzene,butyl-4,4-bis(tert-butylperoxy)-valerate,1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane,tert-butylperoxybenzoate, dibenzoylperoxide,bis(tert-butylperoxyisopropyl)benzene,2,5-dimethyl-2,5-di(benzoylperoxy)hexane,1,1-di(tert-butylperoxy)cyclohexane, 1,1-di(tert amylperoxy)cyclohexane,or any mixtures thereof.

Preferably, the peroxide is selected from2,5-di(tert-butylperoxy)-2,5-dimethyl-hexane,di(tert-butylperoxy-isopropyl)benzene, dicumylperoxide,tert-butylcumylperoxide, di(tert-butyl)peroxide, or mixtures thereof.Most preferably, the peroxide is dicumylperoxide.

It is preferred that cross-linking is effected by including across-linking agent, such as a peroxide in any of the above mentionedembodiments, into the composition.

However, cross-linking may also be achieved by hydrolysable silanegroups which may be present in polyolefin (A). Thus, polyolefin (A) mayalso comprise or consist of a cross-linkable polyolefin containinghydrolysable silane groups.

The hydrolysable silane groups may be introduced into the polyolefin bycopolymerisation of e.g. ethylene monomers with silane group containingcomonomers or by grafting, i.e. by chemical modification of the polymerby addition of silane groups mostly in a radical reaction. Bothtechniques are well known in the art.

In an especially preferred embodiment, polyolefin (A) comprises orconsists of an unsaturated polyolefin, i.e. a polyolefin comprisingcarbon-carbon double bonds, more preferably a polyolefin having a totalamount of carbon-carbon double bonds/1000 carbon atoms of 0.1 or more,more preferably of 0.2 or more, and most preferably more than 0.37.

When used in combination with the unsaturated polyolefin, the term“total amount of carbon-carbon double bonds” refers to those doublebonds originating from vinyl groups, vinylidene groups andtrans-vinylene groups. The amount of each type of double bond ismeasured as indicated in the experimental part.

The incorporation of the total amount of carbon-carbon double bondswithin the polyolefin component enables to accomplish improvedcross-linking properties.

The total amount of vinyl groups is preferably higher than 0.02/1000carbon atoms, more preferably higher than 0.05/1000 carbon atoms, stillmore preferably higher than 0.08/1000 carbon atoms, and most preferablyhigher than 0.11/1000 carbon atoms.

The polyolefin can be unimodal or multimodal, e.g. bimodal.

In the present invention, the polyolefin is preferably unsaturatedpolyolefin, more preferably an unsaturated polyethylene or anunsaturated polypropylene. Most preferably, the unsaturated polyolefinis an unsaturated polyethylene.

In a preferred embodiment, the polyolefin (A) as polyethylene or thepreferably unsaturated polyethylene contains at least 60 wt-% ethylenemonomer units. In other preferred embodiments, the unsaturatedpolyethylene contains at least 70 wt-%, or at least 80 wt-% ethylenemonomer units.

Polyethylene, or preferably unsaturated polyethylene, of low density ispreferred.

Preferably, the unsaturated polyolefin is prepared by copolymerising atleast one olefin monomer with at least one polyunsaturated comonomer.

In a preferred embodiment, the polyunsaturated comonomer consists of astraight carbon chain with at least 8 carbon atoms and at least 4 carbonatoms between the non-conjugated double bonds, of which at least one isterminal.

Ethylene and propylene are preferred olefin monomers. Most preferably,ethylene is used as the olefin monomer.

As a comonomer, a diene compound is preferred, more preferably a C₈ toC₁₄ non-conjugated diene, e.g. 1,7-octadiene, 1,9-decadiene,1,11-dodecadiene, 1,13-tetradecadiene, or mixtures thereof. Furthermore,dienes like 7-methyl-1,6-octadiene, 9-methyl-1,8-decadiene, or mixturesthereof can be mentioned.

Siloxanes having the following formula:CH₂═CH—[Si(CH₃)₂—O]_(n)Si(CH₃)₂—CH═CH₂, wherein n=1 or highercan also be used as a polyunsaturated comonomer. As an example,divinylsiloxanes, e.g. α,ω-divinylsiloxane, can be mentioned.

In addition to the polyunsaturated comonomer, further comonomers canoptionally be used, preferably C₃ to C₁₀ alpha-olefin comonomers withoutfurther unsaturation, such as propylene, 1-butene, 1-hexene,4-methyl-1-pentene, styrene, 1-octene, and/or 1-nonene.

Polyolefin (A) may comprise polar comonomers alternatively or inaddition to non-polar alpha-olefins. Preferably, as polar monomer units,compounds containing hydroxyl groups, alkoxy groups, carbonyl groups,carboxyl groups and ester groups are used.

Still more preferably, the polar monomer units are selected from thegroup of alkyl acrylates, alkyl methacrylates, and vinyl acetates ormixtures therefrom. Further preferred, the comonomers are selected fromC₁- to C₆-alkyl acrylates, C₁- to C₆-alkyl methacrylates, and vinylacetate. Still more preferably, the polar copolymer comprises acopolymer of ethylene with C₁- to C₄-alkyl, such as methyl, ethyl,propyl or butyl acrylates or vinyl acetate, or any mixture thereof.

When preparing the unsaturated polyolefin such as an unsaturatedpolyethylene in a high pressure process, the polymerisation is generallyperformed at pressures in the range of 120 to 350 MPa and attemperatures in the range of 150 to 350° C.

In addition to the components polyolefin (A) and aromatic compound (B),the polymer composition may further comprise components, which may, forexample, be any type of other polymer.

In one embodiment, the polymer composition of the invention furthercomprises a polar copolymer (C).

Polar copolymers (C) preferably are olefin copolymers, more preferablypropylene or ethylene copolymers.

Preferably, the polymer composition further comprises a scorch retarder.In the context of the present invention, a “scorch retarder” is definedto be a compound that reduces the formation of scorch during extrusionof a polymer composition, at typical extrusion temperatures used, ifcompared to the same polymer composition extruded without said compound.Besides scorch retarding properties, the scorch retarder maysimultaneously result in further effects like boosting, i.e. enhancingcross-linking performance during the cross-linking step.

Preferably, the scorch retarder is selected from2,4-diphenyl-4-methyl-1-pentene, substituted or unsubstituteddiphenylethylene, quinone derivatives, hydroquinone derivatives,monofunctional vinyl containing esters and ethers, or mixtures thereof.More preferably, the scorch retarder is selected from2,4-diphenyl-4-methyl-1-pentene, substituted or unsubstituteddiphenylethylene, or mixtures thereof. Most preferably, the scorchretarder is 2,4-diphenyl-4-methyl-1-pentene.

Preferably, the amount of scorch retarder is within the range of 0.005to 1.0 wt.-%, more preferably within the range of 0.01 to 0.8 wt.-%,based on the weight of the cross-linkable polyolefin composition.Further preferred ranges are 0.03 to 0.75 wt-%, 0.05 to 0.70 wt-% and0.07 to 0.50 wt-%, based on the weight of the cross-linkable polyolefincomposition.

The polymer composition may contain further additives, such asantioxidants, stabilisers, processing aids, and/or cross-linkingboosters. As antioxidant, sterically hindered or semi-hindered phenols,aromatic amines, aliphatic sterically hindered amines, organicphosphates, thio compounds, and mixtures thereof, can be mentioned.Typical cross-linking boosters may include compounds having a vinyl oran allyl group, e.g. triallylcyanurate, triallylisocyanurate, and di-,tri- or tetra-acrylates. As further additives, flame retardantadditives, acid scavengers, inorganic fillers, water-tree retardantadditives and other voltage stabilizers can be mentioned.

If an antioxidant, optionally a mixture of two or more antioxidants, isused, the added amount can range from 0.005 to 2.5 wt.-%, based on theweight of the polymer composition.

In general, if a polyethylene is used in the composition, theantioxidant(s) are preferably added in an amount of 0.005 to 1.0 wt.-%,more preferably 0.01 to 0.80 wt.-%, even more preferably 0.05 to 0.60wt.-%, based on the weight of the polymer composition.

Similarly, if a polypropylene is used in the composition, theantioxidant(s) are preferably added in an amount of 0.005 to 2 wt.-%,more preferably 0.01 to 1.5 wt.-%, even more preferably 0.05 to 1 wt.-%,based on the weight of the polymer composition.

Further additives may be present in an amount of 0.001 to 5 wt.-%, morepreferably 0.005 to 3 wt.-%, and still more preferably 0.005 to 2 wt.-%,based on the weight of the polymer composition. Flame retardantadditives and inorganic fillers can be added in higher amounts.

If used for semiconductive layers, the composition may comprise carbonblack in usual amounts, preferably in an amount of from 20 to 60 wt.-%,more preferably from 30 to 50 wt.-%.

The MFR₂ (2.16 kg, 190° C.) of the polymer composition for other thansemiconductor material preferably is from 0.01 to 50 g/10 min, morepreferably is from 0.1 to 20 g/10 min, and most preferably is from 0.2to 10 g/10 min.

The polyolefin (A) and the aromatic compound (B), optionally incombination with one or more optional additives discussed above, can beblended by any conventional blending technique to result in the polymercomposition of the invention.

Where the polymer composition contains an unsaturated polyolefin aspolyolefin (A) then the polymer composition preferably has a totalamount of carbon-carbon double bonds/1000 carbon atoms of more than0.10, more preferably at least 0.20, even more preferably at least 0.30,even more preferably more than 0.35, even more preferably more than0.40, even more preferably more than 0.45, even more preferably morethan 0.50, even more preferably more than 0.55 and most preferably morethan 0.60 carbon-carbon double bonds/1000 carbon atoms. The total amountof double bonds of the cross-linkable polymer composition is based onvinyl, vinylidene and trans-vinylene groups/1000 C-atoms of component(A).

Furthermore, it is preferred that the polymer composition has a totalamount of vinyl groups/1000 carbon atoms of more than 0.02 and morepreferred more than 0.05. It is to be understood that the total amountof vinyl groups in the polymer composition includes also thoseoriginating form of the further polymer components, if present. In otherpreferred embodiments, the polymer composition has a total amount ofvinyl groups/1000 carbon atoms of at least 0.02, more preferably of atleast 0.05, even more preferably of at least 0.08, even more preferablyof at least 0.10, even more preferably of at least 0.15, even morepreferably of at least 0.20, even more preferably of at least 0.25, evenmore preferably of at least 0.30, even more preferably of at least 0.35,even more preferably of at least 0.40, and most preferably of at least0.45.

From the polymer composition described above, a cross-linked compositioncan be prepared by blending with a cross-linking agent, followed bytreatment under cross-linking conditions, thereby increasing thecross-linking level. Cross-linking can be effected by treatment atincreased temperature, e.g. at a temperature of at least 160° C. Whenperoxides are used, cross-linking is generally initiated by increasingthe temperature to the decomposition temperature of the correspondingperoxide. When the peroxide decomposes, radicals are generated from theperoxide. These radicals then initiate the cross-linking reaction.

The total amount of additives in the polyolefin composition according tothe invention is generally 0.3 to 15 wt.-%, preferably 0.6 to 12 wt.-%,more preferably 1 to 10 wt.-%.

From the polymer composition of the present invention, a multilayeredarticle can be prepared wherein at least one layer comprises saidpolymer composition. When cross-linking is initiated, a cross-linkedmultilayered article is obtained. Preferably, the multilayered article(either cross-linked or not) is a cable, preferably a power cable.

In the context of the present invention, a power cable is defined to bea cable transferring energy operating at any voltage. The voltageapplied to the power cable can be alternating (AC), direct (DC), ortransient (impulse).

In a preferred embodiment, the multilayered article is a power cableoperating at voltages higher than 1 kV. In other preferred embodiments,the power cable prepared according to the present invention is operatingat voltages higher than 6 kV.

Most preferably, the power cable prepared according to the presentinvention is designed for operating at voltages higher than 36 kV, andhence is a high or extra high voltage cable, due to the good voltagestabilising effect provided by the invention.

The power cable can be prepared in a process wherein the composition ofthe present invention, optionally in combination with a cross-linkingagent, is applied onto a substrate by extrusion. In such an extrusionprocess, the sequence of mixing the components of the composition can bevaried, as explained below.

According to a preferred embodiment, the polyolefin (A), optionally incombination with further polymer component(s), and the aromatic compound(B) are mixed with each other and possibly with further additives,either on solid pellets or powder of the different polymer components orby melt mixing, followed by forming pellets from the melt.

Subsequently, if used, the cross-linking agent, preferably a peroxide,and optionally a scorch retarder and/or a cross-linking booster areadded to the pellets or powder in a second step. Alternatively, thescorch retarder and/or cross-linking booster could already be added inthe first step, together with the additives. The final pellets are fedto the extruder, e.g. a cable extruder.

According to another preferred embodiment, instead of a two-stepprocess, the polyolefin (A) and any further polymeric component of thecomposition, preferably in the form of pellets or powder, aromaticcompound (B) and, optionally, the further additive(s), cross-linkingagent, and/or scorch retarder, are added to a compounding extruder,single or twin screw. Preferably, the compounding extruder is operatedunder careful temperature control.

According to another preferred embodiment, a mix of component (B) withall other additives, i.e. including antioxidant (s) and cross-linkingagent and optionally a scorch retarder and/or further additives such asa cross-linking booster, are added onto the pellets or powder made ofthe polyolefin (A).

According to another preferred embodiment, pellets made of thepolyolefin (A) and aromatic compound (B), optionally further containingadditional additives, are prepared in a first step, e.g. by melt mixing.These pellets, obtained from the melt mixing, are then fed into thecable extruder. Optionally, subsequently, cross-linking agent andoptionally a scorch retarder and/or a cross-linking booster are eitherfed prior to the hopper, in the hopper or directly into the cableextruder. Alternatively, cross-linking agent and/or scorch retarderand/or cross-linking booster are already added to the pellets beforefeeding these pellets into the cable extruder.

According to another preferred embodiment, pellets made of thepolyolefin (A) and any further polymeric components without anyadditional components are fed to the extruder. Subsequently, component(B) and optionally antioxidant(s), cross-linking agent and optionally ascorch retarder, optionally in combination further additives such as across-linking booster, are either fed in the hopper or directly fed intothe polymeric melt within the cable extruder. The aromatic compound (B)could be added in this step instead, together with the antioxidant(s),cross-linking agent, scorch retarder and the other optional additivesused. Alternatively, at least one of these components, i.e.cross-linking agent, scorch retarder, cross-linking booster,antioxidant(s), aromatic compound (B) or a mixture of these componentsis already added to the pellets before feeding these pellets into thecable extruder.

According to another preferred embodiment, the aromatic compound (B) canalso be provided in a master batch which comprises at least a matrixpolymer and the aromatic compound (B).

The master batch is then added to or mixed with the polyolefin (A) andpossibly further polymer components and further processed in a knownmanner to produce an article, such as power cable.

When producing a power cable by extrusion, the polymer composition canbe applied onto the metallic conductor and/or at least one coating layerthereof, e.g. a semiconductive layer or insulating layer. Typicalextrusion conditions are mentioned in WO 93/08222.

Compounding may be performed by any known compounding process, includingextruding the final product with a screw extruder or a kneader.

The present invention furthermore relates to a wire or cable, comprisingthe polyolefin composition in any of the above described embodiments.

In a preferred embodiment, the invention relates to a medium, high orextra high voltage cable comprising one or more conductors in a cablecore, an inner semiconducting layer, followed by an insulating layer,and then an outer semiconducting layer, wherein at least one of theselayers, preferably the insulating layer, comprises the polyolefincomposition as described above.

One or more of those layers may also be cross-linked.

In one preferred but not limiting embodiment the insulating layers formedium/high/extra high voltage power cables generally have a thicknessof at least 2 mm and the thickness increases with increasing voltage thecable is designed for.

In addition to the semiconductive and insulating layers, further layersmay be present in medium, high or extra high voltage cables, such as ametallic tape or wire shield, and, finally, outermost jacketinglayer(s).

The invention relates furthermore to the use of the polyolefincomposition in any of the above described embodiments for the productionof a layer of a wire or cable, preferably of a layer, more preferably aninsulating layer, of a medium, high or extra high voltage cable.

Still further, the present invention relates to a polyolefin compositioncomprising a voltage stabiliser compound and having a molar fieldstability of at least 2500 kV kg/(mm mol), preferably of at least 3800kV kg/(mm mol), more preferably of at least 4000 kV kg/(mm mol), stillmore preferably at least 5000 kV kg/(mm mol), and most preferably atleast 6500 kV kg/(mm mol), measured in the electrical tree testingmethod indicated below.

Preferred embodiments of this polyolefin composition are thosecomprising the above described components (A) and (B) in any of theirabove-described embodiments and amounts.

Finally, the invention relates to the use, as a voltage stabiliser in apolyolefin composition, of an aromatic compound comprising a, preferablyconsisting of the, structural unit according to the following formula(I):

whereinone or more of the C-atoms in the phenyl rings to which residue R1, R2,R3, R4, R5, R6, R7, or R8 is attached may also be a heteroatom, such asN, in which case the respective residue R1, R2, R3, R4, R5, R6, R7, orR8 is not present;X either is no atom so that there is a direct bond between the twophenyl rings, or is ═C(R11)-, —C(R11)₂-, —C(═Z)—, ═N— or —N(R12)-,Y either is no atom so that there is a direct bond between the twophenyl rings, or is ═C(R13)-, —C(R13)₂-, —C(═Z)—, ═N— or —N(R14)-,Z is a divalent atom such as O,R1, R2, R3, R4, R5, R6, R7, R8 and, if present, R11, R12, R13 and R14independently are hydrogen, or a hydrocarbyl group which may containheteroatoms;or at least two of said R1, R2, R3, R4, R5, R6, R7, R8 or, if present,R11, R12, R13 or R14, together with the ring atoms of the ring system offormula (I) they are attached to, form a further aromatic ornon-aromatic ring fused to the ring system of formula (I), and whereinthe ring system of formula (I) with said at least one fused further ringmay further bear one to eight substituents, R1′ to R8′, each of whichare independently selected from said same groups as R1 to R8;with the provisios that(i) at least one of said R1, R2, R3, R4, R5, R6, R7 or R8, or ifpresent, at least one of said R1′ to R8′, is a hydrocarbyl group whichmay contain hetero atoms; and(ii) at least one of said R1, R2, R3, R4, R5, R6, R7 or R8, or, ifpresent, said R1′ to R8′, R11, R12, R13 or R14, is a hydrocarbyl groupwhich may contain heteroatoms and which has at least 6 non-H atoms;(iii) if any of said R1, R2, R3, R4, R5, R6, R7 or R8, and, if present,any of said R1′ to R8′, R11, R12, R13 or R14 is a hydrocarbyl groupwhich may contain hetero atoms, is attached to an aromatic ring of thecompound according to formula (I), said hydrocarbyl group must be freeof H-atoms in the alpha-position;and/or an aromatic compound with a, preferably consisting of the,structural unit according to the following formula (II):

whereinone or more of the C-atoms in the naphtyl rings to which residue R1, R2,R3, R4, R5, R6, R7, or R8 is attached may also be a trivalent heteroatomsuch as N, in which case the respective residue R1, R2, R3, R4, R5, R6,R7, or R8 is not present;or at least two of said R1, R2, R3, R4, R5, R6, R7 or R8, together withthe ring atoms of the ring system of formula (II) they are attached to,form a further aromatic or non-aromatic ring fused to the ring system offormula (II), and wherein the ring system of formula (II) with said atleast one fused further ring may further bear one to eight substituentsR1′ to R8′;and R1, R2, R3, R4, R5, R6, R7 and R8, and, if present, said R1′ to R8′,have the same meaning and fulfil the same provisios as indicated forformula (I).

The following examples serve to further illustrate the presentinvention, by reference to the figures:

FIG. 1: Results of the electrical testing of the composition of Example1.

FIG. 2: Results of the electrical testing of the composition of Example2.

FIG. 3: Results of the electrical testing of the composition of Example3.

FIG. 4: Results of the electrical testing of the composition of Example4.

FIG. 5: Results of the electrical testing of the composition of Example5.

FIG. 6: The test object used in Examples 1-5 and Comparative Example 1.

EXAMPLES 1. Measurement Methods

a) Melt Flow Rate

The melt flow rate (MFR) is determined according to ISO 1133 and isindicated in g/10 min. The MFR is an indication of the flowability, andhence the processability, of the polymer. The higher the melt flow rate,the lower the viscosity of the polymer. The MFR is determined at 190° C.for polyethylenes and may be determined at different loadings such as2.16 kg (MFR₂) or 21.6 kg (MFR₂₁). The MFR is determined at 230° C. forpolypropylenes.

b) Determination of the Amount of Double Bonds

The procedure for the determination of the amount of double bonds/1000C-atoms is based upon the ASTM D3124-72 method. In that method, adetailed description for the determination of vinylidene groups/1000C-atoms is given based on 2,3-dimethyl-1,3-butadiene. The describedsample preparation procedure has also been applied for the determinationof vinyl groups/1000 C-atoms, vinylidene groups/1000 C-atoms andtrans-vinylene groups/1000 C-atoms in the present invention. However,for the determination of the extinction coefficient for these threetypes of double bonds, the following three compounds have been used:1-decene for vinyl, 2-methyl-1-heptene for vinylidene and trans-4-decenefor trans-vinylene, and the procedure as described in ASTM-D3124 section9 was followed.

The total amount of double bonds was analysed by means of IRspectrometry and given as the amount of vinyl bonds, vinylidene bondsand trans-vinylene bonds, respectively.

Thin films were pressed with a thickness of 0.5-1.0 mm. The actualthickness was measured. FT-IR analysis was performed on a Perkin Elmer2000. Four scans were recorded with a resolution of 4 cm⁻¹.

A base line was drawn from 980 cm⁻¹ to around 840 cm⁻¹. The peak heightswere determined at around 888 cm⁻¹ for vinylidene, around 910 cm⁻¹ forvinyl and around 965 cm⁻¹ for trans-vinylene.

The molar absorptivity, B (in liters/(mole mm)) for each solution isusually calculated using the following equation:

$B = {\frac{1}{C \times L} \times A}$whereC=concentration of the carbon-carbon double bond to be measured(mol/liters)L=cell thickness (mm)A=maximum absorbance (in our case the peak height) of the peak of thetype of carbon-carbon double bond to be measured (mol/liters).

The amount of double bonds/1000 carbon atoms was calculated using thefollowing formulas:vinylidene/1000 C-atoms=(14×A)/(18.24×L×D)

-   -   where the molar absorptivitiy B is 18.24 calculated from the        analyses of the solutions containing 2-methyl-1-heptene.        vinyl/1000 C-atoms=(14×A)/(13.13×L×D)    -   where the molar absorptivitiy B is 13.13 calculated from the        analyses of the solutions containing 1-decene.        trans-vinylene/1000 C-atoms=(14×A)/(15.14×L×D)    -   where the molar absorptivitiy B is 15.14 calculated from the        analyses of the solutions containing trans-4-decene.        wherein        A: absorbance (peak height)        L: film thickness in mm        D: density of the material (g/cm³)        c) Determination of the Vinyl Content Originating from the        Polyunsaturated Compound

The number of vinyl groups originating from the polyunsaturatedcomonomer per 1000 carbon atoms was determined as follows:

Polymer to be determined with respect to vinyl groups originating formthe polyunsaturated comonomer and the reference polymer which the sameexcept without any added polyunsaturated comonomer are produced on thesame reactor, basically using the same conditions, i.e. similartemperature and pressure. Then, it is assumed that the base level ofvinyl groups, i.e. the ones formed by the process without the additionof chain transfer agent resulting in vinyl groups, is the same for bothof the polymers. This base level is then subtracted from the measurednumbers of vinyl groups in polymers, thereby resulting in the number ofvinyl groups/1000 C-atoms, which result from the polyunsaturatedcomonomer.

d) Electrical Tree Testing

The tree field is obtained by a wire-plane electrode configuration (R.Huuva, V. Englund, S. M. Gubanski, et al., “Development of New TestSet-up for Investigation of Electrical Tree Inception in Polyethylene,”presented at Nordic Insulation Conference, Trondheim, 2005; “New TestArrangements for Measuring Electrical Treeing Resistance in Polymers”,Huva R., Chalmers University of Technology, ISSN: 1652-8891). The testobject is then connected to an AC high voltage source prior to beingsubmerged in transformer oil. The voltage is ramped with 0.5 kV/s untilelectrical treeing is achieved. The entire course of events is recordedwith a CCD camera that allows both a visual real time analysis and alater computer analysis using the commercially available programmepackage Abobe Premiere Pro to determine the tree inception field.Testing is done at ambient temperature and humidity.

By applying a Kruskal Wallis test to the data sets, where cross-linkedreference material and the same material with the different voltagestabilisers added, it is seen that the material with voltage stabiliseradded were separated from the reference material to an extent rangingfrom 98.6 to 100%. This means that the two data sets are significantlyseparated.

e) Migration of Voltage Stabilisers

Polyethylene samples were impregnated with the different voltagestabilizers dried and pressed into films. Molding scheme was; 6 minutesat 130° C., the first 3 minutes at 2 kN and the last 3 minutes at 200 kNbefore cooling to room temperature with sustained pressure duringapproximately 15 minutes. The formed films were approximately 150 μmthick.

Each of the films was cut into two strips 20×120 mm and was aged in anElastocon EB01 cell oven at 90° C. with a constant airflow of 5 l/min.For the migration studies polyethylene without peroxide was used, sothat no influence of peroxide decomposition products would influence themeasurements.

The decrease of voltage stabiliser over time in the film strips wasfollowed with FTIR (Fourier Transform Infrared) spectroscopy, measuringthe transmission through the films. A peak at 1509 cm⁻¹ in theFTIR-spectra was attributed to the voltage stabiliser.

After transforming the transmission spectrum into absorbance, the peakat 1509 cm⁻¹ was normalized against the peak at 2016 cm⁻¹, which isattributed to a combination of Raman active twisting and infrared activerocking in both the amorphous and the crystalline phase (A. R. Wedgewoodand J. C. Seferis, “Structural Characterization of Linear Polyethylene,”Pure and Applied Chemistry, vol. 55, pp. 873-892, 1983).

This was done to set an internal standard and the peak height at 1509cm⁻¹ could then be related to the content of voltage stabiliser in thepolymer.

Density

Density of the polymer was measured according to ISO 1183/D.

2. Compositions Produced and Tested

a) Production of Voltage Stabilisers

Unless otherwise specified all the reagents are commercially availableor can be produced according to methods well known in the literature.

Total synthesis of 9-octyl-3,6-bis(4-(octyloxy)phenyl)-carbazole of theinvention Example 3 Synthesis of 3,6-dibromocarbazole according to [1]

Carbazole (15.0 g, 89.7 mmol) and silica (100 g) was mixed indichloromethane and N-bromosuccinimide (33.0 g, 0.185 mol) dissolved indichloromethane was added drop wise and the reaction was carried out for3 h. The silica was filtered off, the filtrate quenched with water, andextracted three times with dichloromethane. The organic phase was thenwashed three times with water, evaporated, and the residual solid wasrecrystallised in ethanol to yield 3,6-dibromocarbazole (9.3 g, 28.6mmol) as green crystals.

Synthesis of 1-bromo-4-(octyloxy)benzene

4-bromophenol (10.46 g, 60.5 mmol), 1-bromooctane (15.43 g, 79.9 mmol)and potassiumcarbonate (90 g, 0.65 mol) in N,N-dimethylformamide and washeated to 90° C. for 4 h and then the potassiumcarbonate was filteredoff. The reaction mixture was quenched with water and extracted threetimes with ether. The ether was then washed three times with 1Mhydrochloric acid (HCl), one time with water, evaporated, and purifiedby distillation to obtain 1-bromo-4-(octyloxy)benzene (15.1 g, 52.9mmol) as a colourless oil.

Synthesis of 4-(octyloxy)phenylboronic acid

1-bromo-4-(octyloxy)benzene (14.64 g, 51.3 mmol) was dissolved in drytetrahydrofuran in nitrogen atmosphere and cooled to −78° C.Butyllithium (50 ml, 80.0 mmol) was then added drop wise and thereaction mixture was let to room temperature. After an hour the mixturewas once again cooled to −78° C. and triethylborate (23.6 g, 0.162 mol)was added drop wise. The reaction mixture was stirred over night at roomtemperature, acidified with 2M HCl, and the organic phase was recovered.It was washed once with water and three times with 1M sodium hydroxideto form a white soapy solid. The combined alkaline phases were acidifiedwith 2M HCl and extracted with ether three times. The combined etherphases were washed with water and dried over magnesium sulphate. Theproduct precipitated in dichloromethane from the reduced ether phase toyield 4-(octyloxy)phenylboronic acid (7.15 g, 28.6 mmol) as a whitesolid.

Synthesis of 3,6-bis(4-(octyloxy)phenyl)-carbazole according to [2]

3,6-dibromocarbazole (3.03 g, 9.32 mmol), 4-(octyloxy)phenylboronic acid(7.14 g, 28.5 mmol), aqueous NaHCO₃ (80 ml), ethanol (120 ml) andtoluene (190 ml) was mixed and degassed with nitrogen for 15 minutesbefore adding the Pd(PPh₃)₄ catalyst (80 mg, 0.07 mmol). The reactionmixture was then brought to reflux at 90° C. for 5 h 20 minutes. It wasquenched with water when reached room temperature and extracted threetimes with ethyl acetate. The combined organic phases were washed withbrine and water and evaporated. The residual solid was dissolved intoluene and precipitated in petroleum ether. The precipitate waspurified using column chromatography with toluene as mobile phase whichyielded 3,6-bis(4-(octyloxy)phenyl)-carbazole (5.42 g, 9.41 mmol) as awhite solid.

Synthesis of 9-octyl-3,6-bis(4-(octyloxy)phenyl)-carbazole according to[3]

3,6-bis(4-(octyloxy)phenyl)-carbazole (4.2 g, 7.29 mmol), 1-bromooctane(4.25 g, 22.0 mmol) and tetrabutylammoniumhydrogensulphate (0.64 g, 1.88mmol) was dissolved in toluene and mixed with NaOH 50% aqueous solution(5.5 ml). The reaction was quenched after 4 h, extracted three timeswith ether, and the combined organic phases was washed with water,evaporated, and purified using column chromatography with a 5/2petroleum ether/toluene mixture as mobile phase. The product wasobtained as colourless oil which crystallized to give9-octyl-3,6-bis(4-(octyloxy)phenyl)-carbazole (1.34 g, 1.95 mmol) aswhite crystals. ¹H-NMR(C₂D₂Cl₄, δ): 0.7-0.9 (m, 9H), 1.15-1.45 (m, 30H),1.758 (m, 4H), 1.848 (m, 2H), 3.957 (t, 4H), 4.251 (t, 2H), 6.951 (d,4H), 7.389 (d, 2H), 7.61 (m, 6H) 8.23 (s, 2H) MS MALDI-TOF (m/z):687.461

Synthesis of 1,4-bis(octyloxy)anthracene-9,10-dione of the invention

1,4-dihydroxyanthracene-9,10-dione (5.0 g, 20.6 mmol), 1-bromooctane(10.0 g, 51.8 mmol), and potassium carbonate (37 g, 0.268 mol) was mixedin N,N-dimethylformamide and heated at 90° C. for 7 h after which thepotassium carbonate was filtered off. The reaction mixture was quenchedwith water and extracted three times with ether. The ether was thenwashed three times with 1M HCl, one time with water, and evaporated togive a dark yellow solid. This solid was recrystallised in methanol toyield 1,4-bis(octyloxy)anthracene-9,10-dione (1.81 g, 3.88 mmol) as ayellow solid. ¹H-NMR (CDCl₃, δ): 0.89 (t, 6H), 1.2-1.4 (m, 16H), 1.53(m, 4H), 1.93 (m, 4H), 4.10 (t, 4H), 7.30 (s, 2H), 7.71 (m, 2H), 8.16(m, 2H) MS MALDI-TOF (m/z): 464.328

Synthesis of N1,N1,N5,N5-tetraoctylnaphthalene-1,5-diamine according to[4] of the invention Example 5

Naphthalene-1,5-diamine (3.14 g, 19.8 mmol), 1-bromooctane (25.25 g,0.130 mol), potassium carbonate (11.79 g, 85.3 mmol), and potassiumiodide (0.05 g, 0.30 mmol) was stirred in dry butanol (150 ml) andheated to 110° C. for 36 h. The reaction was quenched with water andextracted with ether three times. The combined organic phase was washedthree times with water and evaporated to give black oil which wasdistilled under reduced pressure at 90° C. to yield a black tar. Thiswas purified with flash chromatography using hexane as mobile phase toobtain colourless oil which crystallised to yieldN1,N1,N5,N5-tetraoctylnaphthalene-1,5-diamine (2.3 g, 3.79 mmol) aswhite crystals. ¹H-NMR (CDCl₃, δ): 0.85 (t, 12H), 1.0-1.4 (m, 40H),1.4-1.6 (m, 8H), 3.08 (t, 8H), 7.1 (d, 2H), 7.35 (t, 2H), 8.01 (d, 2H)MS MALDI-TOF (m/z): 606.574

Synthesis of 1,5-bis(octyloxy)naphthalene of the invention Example 4

1,5-dihydroxynaphthalene (2.95 g, 18.4 mmol), 1-bromooctane (8.2 g, 42.5mmol), and potassium carbonate (50 g, 0.36 mol) was mixed inN,N-dimethylformamide and heated at 90° C. for 5 h. The potassiumcarbonate was filtered off and the reaction mixture was quenched withwater and extracted two times with ether. The combined organic phase wasthen washed once with 1M HCl, two times with water, and evaporated. Theresidual brown solid was recrystallised in ethanol to form1,5-bis(octyloxy)naphthalene (4.96 g, 12.9 mmol) as brown crystals.¹H-NMR (CDCl₃, δ): 0.89 (t, 6H), 1.2-1.4 (m, 16H), 1.4-1.6 (m, 4H), 1.91(m, 4H), 4.12 (t, 4H), 6.81 (d, 2H), 7.34 (t, 2H), 7.83 (d, 2H) MSMALDI-TOF (m/z): 384.266

Synthesis of 9,10-dioctyloxyanthracene according to [5] of the inventionExample 2

To nitrogen saturated water (100 ml) and dichloromethane (100 ml)9,10-anthraquinone (2.02 g, 9.61 mmol), sodium dithionite (3.39 g, 19.5mmol), and Adogen 464 (3.5 g) was added. This was stirred for 5 minutesbefore addition of sodium hydroxide (3.8 g, 95.0 mmol). The reactionmixture was stirred for an additional 10 min and when it turned deep red1-iodooctane (11.5 g, 47.9 mmol) was added drop wise. The reaction wasstirred at room temperature under nitrogen atmosphere over night. Thephases were separated and the water phase was extracted two times withdichloromethane and then the combined organic phases were washed twotimes with water and evaporated to obtain oil with crystals. These wererecrystallised in ethanol and removed as starting material. After twocrops the ethanol solution was cooled and the ensuing yellow crystalswas purified by column chromatography using dichloromethane as mobilephase to yield 9,10-dioctyloxyanthracene (1.3 g, 2.99 mmol) as a whitesolid. ¹H NMR (CDCl₃, δ): 0.91 (t, 6H), 1.2-1.45 (m, 16H), 1.64 (m, 4H),2.04 (m, 4H), 4.16 (t, 4H), 7.46 (m, 4H), 8.28 (m, 4H) MS MALDI-TOF(m/z): 434.247

Synthesis of 4-methoxy-9-(octyloxy)acridine of the invention Example 1

4-methoxyacridin-9-ol (2.0 g, 8.88 mmol), 1-bromooctane (2.17 g, 11.24mmol), and potassium carbonate (7.91 g, 57.2 mmol) was mixed inN,N-dimethylformamide and heated at 120° C. for 8 h and the potassiumcarbonate was filtered off. The reaction mixture was quenched with waterand extracted two times with ether and the combined organic phases wasthen washed once with 1M HCl, two times with water, and evaporated toobtain a yellow solid. The solid was recrystallised in methanol to give4-methoxy-9-(octyloxy)acridine (0.95 g, 2.82 mmol) as yellow crystals.¹H-NMR (CDCl₃, δ): 0.881 (t, 3H), 1.2-1.4 (m, 10H), 1.924 (m, 2H), 3.985(s, 3H), 4.507 (t, 2H), 7.2-7.3 (m, 3H), 7.621 (d, 1H), 7.707 (m, 1H),8.181 (m, 1H), 8.498 (m, 1H) MS MALDI-TOF (m/z): 337.146

-   [1] Smith, Keith, D. M. James, A. G. Mistry, et al., “A new method    for bromination of carbazoles, [beta]-carbolines and iminodibenzyls    by use of N-bromosuccinimide and silica gel,” Tetrahedron, vol. 48,    pp. 7479-7488, 1992.-   [2] U. Jacquemard, S. Routier, A. Tatibouet, et al., “Synthesis of    diphenylcarbazoles as cytotoxic DNA binding agents,” Organic &    Biomolecular Chemistry, vol. 2, pp. 1476-1483, 2004.-   [3] X. Li, E. A. Mintz, X. R. Bu, et al., “Phase Transfer Catalysis    for Tandem Alkylation of Azo Dyes for the Synthesis of Novel    Multifunctional Molecules,” Tetrahedron, vol. 56, pp. 5785-5791,    2000.-   [4] C. Maertens, Z. Jian-Xin, P. Dubois, et al., “Synthesis and    characterization of end-functionalized oligo-(vinylthiophenes) with    liquid crystal properties,” J. Chem. Soc., Perkin Trans. 2, vol. 4,    pp. 713-718, 1996.-   [5] C. L. Michael Diekers, Dirk M. Guldi, Andreas Hirsch,    “Th-Symmetrical Hexakisadducts of C60 with a Densely Packed pi-Donor    Shell Can Act as Energy- or Electron-Transducing Systems,”    Chemistry—A European Journal, vol. 8, pp. 979-991, 2002.    b) Production and Testing of Compositions

Several compositions including voltage stabilisers for the preparationof insulating layers were prepared and tested together with a referencepolymer without stabiliser according to the following procedures:

Material and Test Set Up for Electrical Tree Testing

In each test for general definitions and for examples of thisapplication the test arrangement for the reference polymer, i.e. thepolymer without the voltage stabilising compounds to be tested, and forthe tested compositions, i.e. the reference polymer containing thevoltage stabilising compounds, was the same.

A commercially available cross-linkable low density polyethylene (LDPE)with a grade name, Supercure™ LS4201S, supplied by Borealis, Sweden,which was prepared by high pressure polymerisation and had a density of0.922 g/cm3 (ISO1872-2/ISO1183-2), MFR2 (ISO 1133, load 2.16 kg, at 190°C.) of 2 g/10 min was used as the polymer for preparing the compositionsto be tested, and also as the reference polymer.

The reference polymer was in a form of pellets which contained dicumylperoxide as a cross-linking agent. The electrode support was made ofcross-linked semi-conducting polyethylene. The electrode used was a 10micrometer tungsten wire supplied by Luma Metall AB.

Sample Preparation for Electrical Tree Testing

Impregnation

The reference polymer pellets for electrical tree testing were ground toa fine powder in a Retsch grinder with a 500 micrometer sieve. For thepreparation of the compositions according to the invention (Examples 1to 5) and the preparation of the comparative composition (ComparativeExample 1), the powder obtained was impregnated with the respective testvoltage stabiliser in a diethyl ether solution for one hour whileagitated every 15 minutes. The diethyl ether was then removed by meansof rotary evaporation and vacuum oven to obtain a dry powder with ahomogeneously distributed voltage stabiliser.

The following compounds were used in the tested compositions as voltagestabilisers in the indicated amounts based on the total composition.

-   Example 1: 4-methoxy-9-(octyloxy)acridine 0.76 wt.-%-   Example 2: 9,10-dioctyloxyanthracene 1 wt.-%-   Example 3: 9-octyl-3,6-bis(4-(octyloxy)phenyl)-carbazole 1.5 wt.-%-   Example 4: 1,5-dioctyloxynaphthalene 2 wt.-%-   Example 5: N1,N1,N5,N5-tetraoctylnaphthalene-1,5-diamine 1 wt.-%-   Comparative Example 1: N-octyl-carbazole 2 wt.-%    Preparation of Test Objects

The test object used here is shown in FIG. 6. It is comprised of a 10micrometer tungsten (1) wire sawn to an electrode support (2) made ofcross-linked semi-conducting polyethylene. This is moulded between twoplaques of the compositions or the reference material to be tested.These plaques are subsequently cross-linked. As moulding machine TP200from Fontijne was used.

The dimensions, molding and cross-linking of the plaques are as follows:The electrode support (2) has a length (5) of 40 mm, a thickness (6) of0.2 mm and a width (7) of with both ends rounded at a radius of 5 mm.The wire is sawn to make a loop where the high and divergent field isproduced. The electrode and its support are moulded between two plaquesof cross-linkable polyethylene, with or without an addition of voltagestabiliser using a two piece mould which holds the electrode support inplace during the whole molding process. The test objects are made inbatches of 10.

The molding scheme for the plaques is 6 minutes at 130° C., the first 3minutes at 2 kN and the last 3 minutes at 200 kN before cooling to roomtemperature with sustained pressure during approximately 15 minutes. Themolding/cross-linking cycle of the test objects starts at 2 kN for 3minutes and goes from 2 kN to 200 kN over 18 minutes with and loadincrease rate of 11 kN/min and is withheld at 200 kN for the rest of theduration of the molding/cross-linking cycle. During the molding cyclethe temperature is set at 130° C. at the beginning of the cycle and atthis temperature for the first six minutes after which it increases to180° C. during 15 minutes with a temperature increase rate of 3.3°C./min and stays at 180° C. for 15 minutes for completing thecross-linking of the moulded plaques before descending to roomtemperature over a period of approximately 30 minutes. The insulationpart of the test object (3) has a thickness (8) of 1.6 mm a width (9) of20 mm and a length of (10) ofapprox. 30 mm after cutting depending onthe wire loop. The distance (4) of the wire loop electrode to the end ofthe insulation part of the test object is 3 mm.

c) Results

1. Electrical Tree Testing

The compositions prepared as well as the reference polymer weresubjected to the electrical tree testing as described above to obtainvalues for their Molar Field Stability (MFS).

Molar Field Stability is a way to describe the efficiency of a voltagestabiliser with reference to the material in which it is added. Theefficiency is the combined increase of the threshold and scale parametertaken from the 3 parameter Weibull statistics (Advanced Power CableTechnology, Tanaka T., Greenwood A., CRC Press Inc., 2000, ISBN:0-8493-5166-9) correlated to the concentration of added voltagestabiliser and can be described as follows:MFS=((Threshold+Scaleparameter)_(VoltageStabiliser)−(Threshold+Scaleparameter)_(Reference))/(mole_(VoltageStabiliser)/kg_(Polymer))

This is also applicable when using 2 parameter Weibull statistics wherethe scale parameter is used, leading to the expression:MFS=(Scaleparameter_(voltageStabiliser)−Scaleparameter_(Reference))/(mole_(VoltageStabiliser)/kg_(Polymer))

In the above equations the subscript “voltage stabiliser” indicates thatthe parameter was obtained from a sample in which the reference polymerhas been impregnated with the respective voltage stabiliser, i.e. fromone of the tested compositions, whereas the subscript “reference”indicates that the parameter was obtained from a sample of the referencepolymer not including a voltage stabiliser.

Molar Field Stability is a modification of Molar Voltage Stability whichhas been used when using double needle setups where a characteristicvoltage usually was obtained. A detailed description of the molarvoltage stability can be found in Chen, C. Ku and Raimond Liepins,Electrical Properties of Polymers, Chapter 4.7 Inhibition of ElectricalTreeing, Carl Hanser Verlag Munich, 1987 (ISBN: 3-446-14280-0).

The values for the Molar Field Stability obtained are given in Table 1:

TABLE 1 Molar Field Stability Example kV kg/(mm mol) Example 1 4220Example 2 5340 Example 3 6760 Example 4 2580 Example 5 >10000Comparative Example 1 12472. Migration Testing

The voltage stabiliser tested was the 1,5-dialkoxy naphthalene withvarying length of the alkoxy chain —OC₄H₉, —OC₈H₁₇ (Example 4) and—OC₁₆H₃₃ added with 2.02 wt.-%, 2.08 wt.-% and 2.58 wt.-%, respectively,to show the migration properties. Different amounts in wt.-% were usedin order to obtain a consistent molar amount.

Table 2 is showing residual concentration as % of initial quantity ofvoltage stabiliser as a mean value from two different filmstrips.

TABLE 2 Days 1 4 6 18 40 1.5-dibutoxynaphthalene 68.9 17.0 7.6 1.1 1.01.5-dioctyloxynaphthalene 86.5 89.2 86.3 85.9 81.81.5-dihexadecyloxynaphthalene 82.2 82.4 84.6 80.3 78.4

The invention claimed is:
 1. A cable comprising a layer made of apolyolefin composition comprising: (i) a polyolefin (A); and (ii) anaromatic compound (B) which is an anthracene derivative having thefollowing structural unit according to the following Formula (I.A):

wherein, in Formula (I.A): R1, R2, R3, R4, R5, R6, R7, R8, R11, and R13are independently hydrogen or a hydrocarbyl group optionally containingheteroatoms selected from the group consisting of Si, N, P, O and S; orat least two adjacent substituents selected from the group consisting ofR1, R2, R3, R4, R5, R6, R7, R8, R11, and R13, together with the carbonatoms of the ring system of formula (I.A) to which the substituents areattached, form a further aromatic or non-aromatic ring fused to the ringsystem of formula (I.A), and wherein the further aromatic ornon-aromatic ring is optionally substituted with 1 to 8 substituents R1′to R8′, independently selected from hydrogen or a hydrocarbyl groupoptionally containing heteroatoms selected from the group consisting ofSi, N, P, O and S; or one or more carbons which form the aromatic ringof Formula (IA) is heteroatom, N, and the corresponding R group isabsent; with the provisos that: (a) at least one of said R1, R2, R3, R4,R5, R6, R7, R8, R11 or R13 or, if present, R1′ to R8′ is selected fromthe groups of —O(R9) and —NR(R10)2, wherein R9 and R10 are alkyl groupswith at least 6 C-atoms which may or may not contain a functional groupat the end which, if present, is a —CH═CH2, a halogen, a hydroxyl, acarboxylic acid or acid halide group; and (b) if any of R1, R2, R3, R4,R5, R6, R7, R8, R11 or R13 or, if present, any of R1′ to R8′ is ahydrocarbyl group optionally containing heteroatoms selected from thegroup consisting of Si, N, P, O and S, and is attached to an aromaticring of the compound according to Formula (I.A), said hydrocarbyl grouplacks H-atoms in the alpha-position.
 2. The cable of claim 1, whereinthe aromatic compound (B) is 9,10-dioctyloxyanthracene.
 3. The cable ofclaim 1, wherein the polyolefin (A) comprises a polyethylene orpolypropylene.
 4. The cable of claim 1, wherein the polyolefin (A)comprises a polyethylene which has been produced by a high pressureprocess using free radical polymerization resulting in low densitypolyethylene (LDPE).
 5. The cable of claim 1, wherein the layer made ofthe polyolefin composition is an insulation layer.
 6. A medium, high orextra high voltage cable comprising one or more conductors in a cablecore, an inner semiconductive layer, followed by an insulation layer andthen an outer semiconductive layer, wherein at least one of these layerscomprises a polyolefin composition comprising: (i) a polyolefin (A); and(ii) an aromatic compound (B) which is an anthracene derivative havingthe following structural unit according to the following Formula (I.A):

wherein, in Formula (I.A): R1, R2, R3, R4, R5, R6, R7, R8, R11, and R13are independently hydrogen or a hydrocarbyl group optionally containingheteroatoms selected from the group consisting of Si, N, P, O and S; orat least two adjacent substituents selected from the group consisting ofR1, R2, R3, R4, R5, R6, R7, R8, R11, and R13, together with the carbonatoms of the ring system of formula (I.A) to which the substituents areattached, form a further aromatic or non-aromatic ring fused to the ringsystem of formula (I.A), and wherein the further aromatic ornon-aromatic ring is optionally substituted with 1 to 8 substituents R1′to R8′, independently selected from hydrogen or a hydrocarbyl groupoptionally containing heteroatoms selected from the group consisting ofSi, N, P, O and S; or one or more carbons which form the aromatic ringof Formula heteroatom, N, and the corresponding R group is absent; withthe provisos that: (a) at least one of said R1, R2, R3, R4, R5, R6, R7,R8, R11 or R13 or, if present, R1′ to R8′ is selected from the groups of—O(R9) and —NR(R10)2, wherein R9 and R10 are alkyl groups with at least6 C-atoms which may or may not contain a functional group at the endwhich, if present, is a —CH═CH2, a halogen, a hydroxyl, a carboxylicacid or acid halide group; and (b) if any of R1, R2, R3, R4, R5, R6, R7,R8, R11 or R13 or, if present, any of R1′ to R8′ is a hydrocarbyl groupoptionally containing heteroatoms selected from the group consisting ofSi, N, P, O and S, and is attached to an aromatic ring of the compoundaccording to Formula (I.A), said hydrocarbyl group lacks H-atoms in thealpha-position.
 7. The cable of claim 6, wherein the aromatic compound(B) is 9,10-dioctyloxyanthracene.
 8. The cable of claim 6, wherein thepolyolefin (A) comprises a polyethylene or polypropylene.
 9. The cableof claim 6, wherein the polyolefin (A) comprises a polyethylene whichhas been produced by a high pressure process using free radicalpolymerization resulting in low density polyethylene (LDPE).
 10. Thecable of claim 6, wherein the insulation layer comprises the polyolefincomposition.